Obesity is a modifiable risk factor for knee osteoarthritis (OA), and weight loss is an effective non- pharmacologic treatment to reduce pain. Recently, we determined that under ideal, highly controlled circumstances, a diet-induced weight loss of 10% combined with exercise was significantly better at reducing pain than either intervention alone. Compared to previous long-term weight loss and exercise trials of knee OA, our diet-induced weight loss and exercise group was twice as effective at relieving pain. Whether our groundbreaking results can be generalized to less rigorously monitored patient cohorts is unknown. Thus, the policy relevant and clinically significant question is: How can we adapt this successful solution to a pervasive public health problem so that it provides a cost-effective intervention for real-world clinical and community settings? This study aims to develop and to demonstrate the effectiveness of a systematic, practical, cost-effective diet-induced weight loss and exercise intervention that communities can implement to reduce pain and improve other clinical outcomes in knee OA patients. This pragmatic community-based trial will determine if the important benefits realized by participants in our previous trial translate to rea-world settings. Participants will be 820 ambulatory, community-dwelling, overweight and obese (BMI = 27 kg/m2) men and women aged = 50 years who meet the American College of Rheumatology clinical criteria for knee OA which includes knee pain on most days of the week plus at least 3 of the following 6: age = 50 years; stiffness < 30 min/day; crepitus; bony tenderness; bony enlargement; no palpable warmth. The primary aim is to determine whether a pragmatic, community-based 18-month diet-induced weight loss and exercise intervention implemented in three North Carolina counties with diverse residential (from urban to rural) and socioeconomic composition significantly decreases knee pain in overweight and obese adults with knee OA relative to an attention control group. Secondary aims will determine whether this intervention improves self-reported function, health-related quality of life, and mobility. We will also establish the cost-effectiveness of this pragmatic, community-based intervention by conducting cost-effectiveness and budgetary impact analyses using data from the current trial in a validated computer-simulated model of knee OA. Many physicians who treat people with knee OA have no practical means to implement weight loss and exercise treatments. This study is significant in that it will test the effectiveness of a long-awaited and much needed community program that will serve as a blueprint for clinicians and public health officials in urban and rura communities to implement a weight loss and exercise program designed to reduce knee pain and improve other clinical outcomes in overweight and obese adults with knee OA.